of course! you mean a soft C (s) or a hard C (k)
I'll give you examples of both.

Cook (hard C)
Cesspool (Soft C)
Celebrate (Soft C)
Calendar (Hard C) 
Calibrate (Hard C) 

Each word corresponds with a vowel in this instance. Is there anything outstanding you can notice?
 

This is a pronunciation/writing rule borrowed directly from French.

<em>ca</em>, <em>co</em>, <em>cu</em> = ka, ko, k(y)u  (capable, company, occupy)

(The <em>y</em> sound you might hear before <em>u</em> comes from the difference between the French <em>u</em> and the English <em>u</em>... but that's another story!)

<em>ci</em>, <em>ce</em>, <em>cy</em> = si, se, <em>sy</em>  (precision, certainly, bicycle)

Of course, this basically applies to loanwords from French - there are many of them in English!

That was a really clear answer Stephanie with excellent examples. I can do no better 

Hi Faatma:

 I think  first link at the following website will help you: 

http://rbeaudoin333.homestead.com/hardsoftc_g_1.html

 You might read over it with a language partner.

Yah I mean that:)  Thanks Stephanie